1. Field of the Invention
The invention is based on a plastic vane for a vane cell vacuum pump in which the vane has a body portion and a terminal part of different materials.
2. Description of the Prior Art
From German Utility Model DE-GM 75 03 397, a cell compressor is known that is equipped with plastic laminations or vanes. While the part of the laminations associated with the rotor of the cell compressor comprises a low-grade material, the terminal part of the laminations, which is associated with a jacket wall of the compressor housing, should conversely comprise a highly wear-resistant material. The parts of the laminations are produced separately from one another and joined together by methods such as adhesive bonding, riveting and welding. The two lamination parts can also be pressed together already during the production process. A multi-part lamination structure has the disadvantage that the individual tolerances of the lamination parts add up. This is especially harmful if laminations with parts of highly wear-resistant material disposed on both ends are produced in this way. Laminations or vanes produced in this way reach through the rotor and are meant to engage the housing sealingly on both ends, as is known for instance from U.S. Pat. No. 3,877,851.
The vane of the invention is advantageous in the sense that on the one hand, there is no need to mount separately produced individual parts, and on the other, the injection-molding tool determines the final shape of the vane replicably, with relatively close tolerances.
In one embodiment a structure of the vane is defined in which the body of the vane is first created by injection molding, transfer molding, or compression molding, and then, in the same injection-molding tool or a different one, the terminal part of the vane is completed.
A further feature of the invention is advantageous in the sense that on the one hand the dimensional accuracy of the vane is improved by a reduced influence of material shrinkage at the terminal part, and on the other, if the material of the terminal part is expensive, the costs of the vane can be kept low.
A joining of the parts can be accomplished in a simple way in the course of producing the vane, especially if with the materials used for the body and the terminal part of the vane, material engagement is not attainable.
With the heat treatment of the body of the vane an increase in the strength of the vane is attained by means of the maximum attainable, three-dimensional degree of cross-linking of the molecular structures and a constancy in the vane geometry by a reduction of tension in the microstructure of the material, as well as an avoidance of aftershrinkage.